(a) Field of the invention
The present invention relates to an improvement of a ranging drum shearer which is used as a coal mining machine in a pit having a long-walled pit face and more particularly to a coal mining machine provided with a plurality of cutting drums interacting with one another so as to make it possible to adjust the range of coal mining height and therefore to easily attain a coal mining operation according to the change of a coal bed.
(B) Description of the prior art
Conventional ranging drum shearers which have been used as a coal mining machine can be generally classified, according to the number of cutting drums provided, into a single ranging drum shearer having a ranging arm with a cutting drum provided at one end of the shearer and a double ranging drum shearer having a ranging arm with a cutting drum provided, respectively, at both ends of the shearer. However, these shearers of both types have the following disadvantages since they are limited in the outer diameter of their cutting drums from the viewpoint of mechanical strength.
In the case of the single ranging drum shearer provided with only one cutting drum, it is often that the pit face of a pit cannot be cut in one travel of the shearer, thus causing the shearer to be travelled forwards and backwards along the pit face, varying the position of the cutting drum in its level every forward and and backward travels. Further, since the cutting drum is provided only at one end of the shearer, the cutting operation cannot reach the foremost end of the pit face and therefore an additional operation such as hand cutting or the one by a different cutting machine is absolutely needed, thus lowering the efficiency of coal mining operation considerably.
On the other hand, in the case of the double ranging drum shearer, the cutting drums, each provided at both ends of the shearer respectively, are arranged with the one at an upper position and with the other at a lower position so that when the height of a coal bed is less than two times the outer diameter of a cutting drum, the coal bed can be perfectly cut in its whole level in one travel of the shearer. However, since the cutting drums are provided apart from each other at both ends of the shearer, only one travel of the shearer will leave the foremost end portion of the pit face not cut by either of the upper and lower cutting drums, thus making it necessary to again travel the shearer with the upper and lower cutting drums turned upside down, so as to cut the foremost end portion left. Further, when the floor of the coal bed is uneven, it is difficult for the double ranging drum shearer to attain a cutting operation keeping the coal mining height constant. Furthermore, since the height of the coal bed which can be cut by one travel of the shearer is limited to the sum of the outer diameters of two cutting drums and there is a limit in the outer diameter of the cutting drum as stated above, the coal bed having a height higher than the sum must be cut by the reciprocation of the shearer as in the case of the single ranging drum shearer or it is necessary to employ a blasting method or a method by which the coal mining operation is achieved at an upper and a lower pit faces respectively, thus resulting in an unsatisfactory efficiency of the coal mining operation. And furthermore, the operator of the shearer must always keep his eyes on the cutting drum cutting the floor side of the coal bed so that when the shearer is travelling windward, he is forced to work at the leeward side and in the coal dust, which is unhealthy to him as well as dangerous to his operation of the shearer, particularly when the coal dust is so thick as to make his visibility extremely worse. Water spraying intended to avoid this has not gained satisfactory effect.